High frequency receiver



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Patented July 7, 1942 HIGH FREQUENCY RECEIVER Richard F. Shea,Bridgeport, Conn., assignor to General Electric Company, a corporationof New York Application August 22, 1940, Serial No. 353,665

(Cl. Z50- 20) 9 Claims.

My invention relates to high frequency receivers and more particularlyto receivers adapted, for example, to home radio reception employingboth unicontrolled tuning means variable over a desired range, and xedtuning means to tune the receiver to fixed frequencies in said range,the fixed frequencies being selected by switches, such as the pushbuttons of ordinary. household receivers. 2

It has for one of its objects to effect certain economies in theconstruction of such receivers.

A further object of my invention is to provide means to avoid employmentof fixed tuning means in the interstage circuits operating at thereceived frequency.

A further object of my invention s to provide means whereby when thereceiver is adjusted for push button operation, the interstage tunedcircuits are rendered ineiective, or removed from the circuit, and anuntuned broad band pass network is utilized to furnish the desiredinterstage coupling.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which the single gure represents anembodiment of my invention.

Referring to the drawing I have illustrated therein a portion of a radioreceiver comprising a radio frequency amplier employing an electrondischarge device I, a local oscillator 2, and a converter 3 forconverting the received oscillations and the oscillations produced bythe local oscillator 2 to oscillations of xed frequencygor all receivedfrequencies. The output of this converter, which is of constantfrequency for all received frequencies, is supplied to a tuned circuit 4tuned to this constant frequency which in a superheterodyne receiver isordinarily known as the intermediate frequency. Those portions of thereceiver subsequent to the circuit 4 are not shown in the drawing sincetheir nature does not pertain to my present invention.

The control grid of the radio frequency amplifier I is connected througha coupling condenser 5, the movable contact 'I of a `switch. designatedon the drawing as S, and a tuning condenser 8, to the cathode of thedischarge device. Similarly, the control grid 9 of the converter 3 isconnected through movable contact I0 of the switch S and tuningcondenser I I to the cathode of the discharge device 3. Likewise, thecontrol grid I2 of the local oscillator is connected through the gridcondenser I3 thereof, movable contact I4 of the switch S and tuningcondenser I 5 to the cathode of the discharge device 2. The tuningcondensers 8. II, I5 are arranged for unicontrolas indicated by thedotted lines shown on the drawing interconnecting these differentcondensers, and comprise the ordinary means for tuning respectively theinput circuit of the amplier, the coupling circuit between the amplierand the converter, and the local oscillator thereby to select thedesired stations which are to be received.

The switch S is the band change switch of the receiver and may be of theordinary Yaxley wafer construction but for purposes of illustration isshown on the drawing as having a plurality of contacts such as thecontacts Ii, 1, Ill, I4 already mentioned and others presently to bementioned, all interconnected for unicontrol as indicated by the dottedlines to which the character S has been applied on the drawing.

This switch has four positions. In the position shown it connects thereceiver for tuning by means of the unicontrolled variable ciondensers8, II, I5 over a range of frequencies which may be the broadcast band.This may be designated the B position of the switch. It may be moved tothe left to either of two positions C and D in which it connects thereceiver for tuning over either of two higher frequency bands by meansof condenser 8, II, I5, or it may be tuned to the right to position A inwhich it disconnects condensers 8, II, I5 from the circuit of thereceiver and substitutes in the place of condenser 8 a fixed condenserI'I plus the push button switching mechanism I8 shown at the top of thedrawing. It also substitutes for condenser I5 the xed condenser I 5'shunted by an inductance I9 connected thereto through certain switchesof the push button mechanism I8.

It also, in its A position, disconnects condenser I I from the receivercircuit so that the inductive coupling circuit between amplier I andconverter 3 is untuned and rendered ineiective, and at the same time itdisconnects a xed by-pass condenser 20 from the receiver thereby torender effective between the amplifier I and the converter 3 a broadband resistance capacity coupling comprising elements 26, 30, 56 and 58,which will be more particularly mentioned hereinafter.

The circuits of the receiver in each position of the switch S will nowbe described in detail. With the switch in the position B, which is thatshown on the drawing, the input circuit to the amplifier I extendsthrough the condenser 5, variable contact 5 of the switch S in its Bposition and loop antenna 2l to ground 22 and thence back to the cathodeof ampliner I. The loop antenna 2| is designed for operation in thebroadcast band which extends from about 550 to 1700 kilocycles andis,tuned by the variable condenser 8 and the trimmer condenser 23.

The anode circuit of the amplifier extends through the primary winding24 of a transformer 25 and through resistance 2i to the source of highvoltage operating potential for the receiver, the positive terminal ofwhich is indicated by the line 21, and the negative terminal of whichmay be grounded. With the switch S in the position shown the secondarywinding 28 of this transformer is connected by means of contacts 29 andI0 thereof across the variable condenser II, these movable contacts 29,I3 being connected to the control grid of the converter 3. This controlgrid is connected through the winding 2B and a resistance 30 to the bus3i which may be the automatic volume control bus of the receive This busincludes a resistance 32 and is connected to ground through a condenser33 which elements may comprise an ordinary automatic volume controlfilter circuit. The secondary winding 28 of transformer 25 is tuned bymeans of condenser II and trimmer condenser 34.

At the same time the cathode of the local oscillator 2 is connectedthrough movable contact 35 of the switch S to an intermediate point onthe tuned circuit 35, one terminal of which is connected to ground andthence through condenser 31 to the anode of the discharge device 2, andthe opposite terminal of which is connected through a series alignmentcondenser 38, movable contact 39 of the switch, and grid condenser I3 tothe grid of the oscillator 2. This grid is connected to ground throughthe ordinary oscillator grid resistance 40. The tuned circuit 36 istuned over the -band of frequencies corresponding to the broadcast bandof received frequencies by means of the condenser I5.

With the circuits as thus described the receiver is adapted forreception of the broadcast band of frequencies by means of the loop 2|and by variation of the tuning of the receiver by means oi' condensers8, II; I5.

The loop antenna 2| is provided with a tap connection 4I which isconnected through an inductance 42 and contact 43 of the switch to anantenna 44 which may be the ordinary outdoor antenna for home receptionwhich may be utilized in situations where the directvity of the loop 2|is not highly important.

Such a connection of an ordinary outdoor antenna and loop is shown andclaimed in application Serial No. 238,417, led November 2, 1938 byGeorge W. Fyler entitled Radio receivers, now Patent No. 2,222,709,issued November 26, 1940, and which is assigned to the assignee of mypresent application. The antenna is connected to ground through aresistance 45 which coacts with the inductance 42 to aid in thesuppression of image frequencies.

If the switch be moved to its C position, the input to the amplifier Iis changed by substitution of loop 43 for loop 2|, this loop being tunedby the condenser l and trimmer 41 for reception of a higher band offrequencies. An inter- II and trimmer 53' over said higher frequencymediate point on the loop 48 is also connected through contact 43 of theswitch to the antenna 44, but in this case no .means for suppressingimage frequencies is employed.

A second primary winding 41 of the interstage coupling transformer 25 isnow connected in parallel with the primary winding 24 'by means ofcontact 48 of the switch and secondary winding 28 is now removed fromthe grid circuit of the converter and in its place is substitutedsecondary winding 49, this winding being tuned by condenser I I' andtrimmer 49.

The oscillator circuit is now changed by contact 39 of the switch bysubstitution of oscillating circuit 50 for the oscillating circuit 38.

If switch S be moved to its D position, loop 5I is substituted in placeof loop 46, this loop being tuned by means of condenser 8 and trimmer 52over a still higher band of frequencies. Primary winding 41 is nowremoved from the output circuit of the discharge device II leaving onlyprimary winding 24. Secondary winding 53 is now inserted by means ofcontact 29 of the switch in the grid circuit of the converter, thissecondary winding being tuned by condenser band. In the oscillatorcircuit the tuned circuit 54 is substituted for the tuned circuit 50.

In all positions B, C and D of switch S the coupling between the radioamplifier I and converter 3 is effected practically entirely by thetransformer 25 and condenser 58. Resistance 25 may desirably be of abouttwenty-two hundred ohms and has connected in parallel with it the seriescombination of coupling condenser 56 and by-pass condensers 2U and 2li'and hence it has very small effect upon coupling between the circuits ofthe two discharge devices. Resistance Y30 is shunted by the pathcomprising condenser 20 connected between its upper terminal and groundand condenser 33 connected between its lower terminal and ground, andthus has practially no eifect on the coupling between the circuits.Condenser 55 is of about two or three hundred micro-microfarads.

Ii.' the switch S be moved to the right, to the A position, the tuningcondensers 8, I.I, I5 are all removed from the circuit and the broadcastband loop 2i is restored to the circuit. The grid circuit of theampliiier I is now tuned by means of a condenser I1 which is connectedthereto through the various contacts of the push button assembly I8.Similarly, the tuned circuit 38 of the oscillator is now restored to itscircuit relation with discharge device 2 and has connected across it theinductance I9. This circuit extends from ground through the circuit 3B,movable contact 39 of switch S, movable contact I4 of switch S,conductor 51, upper contacts of the lower armatures of push buttonassembly I8 and inductance I9 to ground, this circuit being tuned to adesired frequency by adjustment of inductance I9. Condenser I'I isremoved from circuit by contact III, and therefore, the transformer 25is no longer tuned thereby. The by-pass condenser 20 is open crcuted bycontact 55 o1' the switch. In this way the transformer is renderedsubstantially ineffective as a coupling means between the amplier andconverter but resistances 26 and 30 are now effective as couplingresistors in a coupling network comprising these resistors andcondensers 56 and 58, the latter of which is connected directly betweenthe anode of ampliner I and the control grid of the converter.Theseelements 26, 30, 5E and 58 may be proportioned to act as a wideband coupling network which is effective to transmit any frequency inthe broadcast band or which may be selected by the push button assembly.

The various stations which may now be selected are determined by thepush buttons 60, 6|, 62, 63, 64, 65 on the push button assembly. Pushbuttons 6U to 64 are each provided with two movable contacts orarmatures, one of which is connected in the amplifier input circuit andthe other in the oscillator circuit, and each armature has twopositions, namely, the position shown in the drawing and a lowerposition in which it is retained by means of a latch member 6B havingslots 61 therein through which the push button members extend. The latch66 is biased by means of a spring 68 against the push button. Each pushbutton member is also provided with a pawl 69 which cooperates with theslot 61 on the latch so that whenthe push button is operated `downwardlythe latch is moved to the right until the pawl has completely passed thelatch. The latch then returns to its initial position latching theoperated push button in its lower position. When the latch is thusoperated, any other push button previously operated to its lowerposition, is released. Push button 65 is not :provided with any contactarmatures but operates when pressed to restore buttons 60 to 64 to theposition shown in the drawing inserting -condenser I1 and coil |9 intheir respective circuits.

It will be understood that the mechanical details of this push buttonassembly just described are described solely by Way of illustrating oneform of push button assembly which may be used. Any of the forms nowcommonly in use may be employed.

When push button 60 is operated to its downward position, the inputcircuit of the receiver is tuned to a frequency determined by fixedcondenser and the local oscillator is tuned to a frequency determined byinductance 1|. When push button 6| is operated, push button 6G isreleased and the input of the receiver is then tuned to a stationdetermined by condenser 12 and the local oscillator is tuned to afrequency determined by inductance 13. The condensers I1, 10, 12, etc.,may, if desired, be of any suitable type variable for purposes ofinitial adjustment and the inductances I9, 1|, 13, etc., may be of theiron core type in which the core is variable for variation of the tuningof the oscillator over a desired range for purposes of initialadjustment.

It will be seen that by the use of my invention i it is unnecessary toprovide on the switch assembly I8 an additional set of movable contactsand associated tuning reactances controlled by the push buttons toeffect the tuning of the interstage coupling circuit between amplifierand converter 3, this complication being avoided by the simple use ofthe resistance capacity coupling circuit 26, 30, 56, 58, which isrendered effective by means of conta-ct 55 of the switch. Thus, when thereceiver is adjusted for push button tuning, Wide band coupling is usedin the interstage circuits and tuning thereof to the different stationspreset by the push button assembly is avoided.

In addition, with switch S adjusted to either the B or C positionsresistance and condenser 20 serve as an additional filter in theautomatic volume control circuit to the grid 9 of the converter. It aidsin reducing audio frequency or intermediate frequency, feed back fromthe automatic volume control rectifier, now commonly employed in suchvreceivers,'through conductor 3| now resistance 30 to the grid 9 of theconverter. When switch S is in the D position, for operation in thehighest frequency band the lower terminal of resistance 30 is groundedand the automatic volume control circuit to grid 9 of the converter isinterrupted by contact of the switch. This is desirable because in theupper portion of the D frequency band voltage of the frequency of theoscillator appears in considerable quantity on the grid 9 producingrectication and unidirectional voltage on the filter resistors in theautomatic volume control circuit which tends to bias the amplifier andconverter to cut off. This is avoided by interrupting the circuit at thecontact 80.

While I have shown a particular embodiment of my invention, it will, ofcourse, be understood that I do not wish to be limited thereto sincemany modifications both in the circuit arrangement and in theinstrumentalities employed may be made and I contemplate by the appendedclaims to cover any such modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a pair of electron discharge amplifiers, couplingmeans between said amplifiers tunable over a range of frequencim,untuned means coupling said amplifiers over the same range offrequencies, and switching means for rendering said tunable couplingmeans and said untuned coupling means alternatively effective over saidrange of frequencies.

2. In combination, a pair of electron discharge amplifiers, one of saidamplifiers having an outputcirouit, and the other of said amplifiershaving an input circuit, a coupling between said circuits, a resistancein said output circuit, means to tune said coupling to a desiredfrequency, means to render said tuning means ineffective and means tosupply potential variations on said resistance to said input circuit atall frequencies over a Wide range.

3. In combination, a pair of electron discharge amplifiers, tunablecoupling means between the output electrodes of one of said amplifiersand the input electrodes of the other amplifier, a circuit between saidoutput electrodes including an element of said coupling means and aresistance, a shunt path around said resistance, means connected to saidcoupling means to tune said coupling means to any desired frequency in awide band of frequencies, means to render said last means ineffectiveand to interrupt said shunt path, and means to supply the potentialvariations on said resistance to said input electrodes.

4. In combination, a pair of electron discharge amplifiers, couplingmeans between said amplifiers, means to supply operating potential tothe anode of one of said amplifiers through a resistance and an elementof said coupling means, means to supply bias potential to a grid of theother of said amplifiers through a resistance and an element of saidcoupling means,a shunt path between the cathodes of said dischargedevices and the points between said resistances and said reactivecoupling means for currents of the frequency at which said amplifieroperates a capacitance between said anode and grid, means to tune saidcoupling means to said frequency,

means to disable said tuning means and simultaneously to interrupt saidshunt path, said resistances and said capacitance being proportioned tooperate as a resistance capacity coupling network between saidamplifiers over a wide range of frequencies. q

5. In combination, an electron discharge device having an anode circuitincluding the primary winding of a transformer and a resistance inseries, a second electron discharge device having a grid circuitincluding a secondary winding of said transformer and a resistance inseries, av

capacitance between the anode of said first electron discharge deviceand the grid of said second electron discharge device, a low impedancepath between the cathodes of said discharge devices and the points onsaid circuits between said windings and the respective resistances forfrequencies at which said discharge devices operate, and means tointerrupt said path, said resistances and said capacity beingproportioned to act as a resistance-capacity coupling between saiddischarge devices when said path is interrupted.

6. In combination, an electron discharge device having an anode circuitincluding the primary winding of a transformer and a resistance inseries, a second electron discharge device having a grid circuitincluding a secondary winding of said transformer and a resistance inseries, a capacitance between the anode of said first electron dischargedevice and the grid of said I,

second electron discharge device, a low impedance path between thecathodes of said discharge devices and the points on said circuitsbetween said windings and the respective resistances for frequencies atwhich said discharge devices operate, a tuning reactance connected tosaid transformer to tune it to the frequency at which said dischargedevices operate, and means to discon` means alternatively operative, thecombination of a tuned coupling network between two stages in saidreceiver, said first tuning means including means to tune said couplingnetwork to select any frequency in said range, a normally ineffectivebroad band coupling network between said stages, and means responsive tooperation of said switching means to render said fixed frequency tuningmeans eective, to render said tuned coupling network ineffective and torender said broad band coupling network effective.

8. The combination, in a radio receiver having a tunable couplingnetwork between different electron discharge stages of said receiver, ofmeans to tune said receiver over a band of frequencies, said meansincluding means to tune said network over said band of frequencies,switching means arranged to tune said receiver to any one of a pluralityof fixed frequencies in said band, means to render said tuning means andswitching means alternatively effective, a capacitive interstagecoupling network, and means responsive to operation of said last meansto render said switching means effective, to render said tunablecoupling network ineffective and to render said capacitive couplingnetwork effective between said stages.

9. In a high frequency receiver having a received frequency amplifier, alocal heterodyne oscillator, and a converter to combine the receivedoscillations amplified by said amplifier with the oscillations producedby said local oscillator to produce additional oscillations, a tunedcoupling between said amplifier and converter, said amplifier, tunedcoupling and local oscillator being tunable over respective ranges offrequencies such that said additional oscillations are of constantfrequency for all received frequencies, the combination of an untunedcoupling between said amplifier and converter, switching means to tunesaid amplifier and oscillator to any one of a plurality of fixedfrequencies throughout their respective ranges, and means responsive tooperation of said last means to render said tuned coupling ineffectiveand said untuned coupling effective between said amplifier andconverter.

RICHARD F. SHEA.

